In the production of acrylonitrile by the catalytic ammoxidation of propylene with ammonia and oxygen, a crude acetonitrile byproduct is produced. This material normally is composed of, on a weight basis, about 52% acetonitrile, 43.6% water, 2.5% HCN, 0.5% acrylonitrile and 1.3% other organics such as oxazole, allyl alcohol, acetone and propionitrile.
Traditionally, this crude acetonitrile byproduct has simply been disposed of by incineration. More recently, however, it has been processed so as to recover acetonitrile as a valuable byproduct.
In this processing, the crude acetonitrile is first distilled to drive off HCN. Then, the HCN-free material is distilled to produce an acetonitrile/water azeotrope containing about 25% water, which in turn is then slurried with anhydrous calcium chloride. The anhydrous calcium chloride takes up most of the water in the azeotrope to produce an acetonitrile/water mixture containing about 3% to 5% water, which in turn is distilled to produce a pure acetonitrile product.
The conventional process for recovering the acetonitrile produces a relatively large amount of waste calcium chloride which must be disposed of and further is accomplished in a batch operation which leads to various operational difficulties.
Accordingly, it is an object of the present invention to provide a new technique for recovering acetonitrile from a crude acetonitrile process stream which is simple and straightforward to carry out and can be conducted on a continuous basis.